1. Technical Field of the Invention
The subject invention is a security system which employs an optical key shape reader. The system is particularly suited for use in automobiles and other motor vehicles.
2. Description of the Prior Art
Automobile theft has become an increasingly prevalent problem for our society. In particular, expensive sports and luxury cars have become targets for thieves. Simple key locks for such vehicles are no match for experienced thieves who are able to enter and start the vehicles in a matter of seconds.
In an effort to increase the security of automobiles, efforts have been made to develop new, high security systems. One such system was introduced by General Motors Corporation in 1986 for its Corvette model line. The system is called a Vehicle Anti Theft System or VATS. This system is described in detail in a paper entitled "The Vehicle Anti-Theft System--VATS" by Schroeder et al., SAE Technical Paper Series, 1986.
As described therein, VATS uses a modified ignition key with an electrical resistor pellet embedded in the upper shaft of a standard key. The electrical resistor has one of fifteen possible resistance values. In order to start the car, the VATS ignition key must have the proper cuts, like any conventional key, as well as the correct resistance value. The resistance of the pellet is sensed by electrical contacts built into the ignition lock. These contacts are connected by wires to a remote VATS module where the decision is made if the correct resistor pellet is in the key. The significant feature about VATS is that the decision to accept or reject the key is made remote from the ignition lock and steering column. This defeats the most common mode of automotive theft which is to use a hammer to crack open the plastic housing that surrounds the steering column and ignition lock, followed by the use of a screw driver to force the ignition mechanical linkages to start the ignition. The VATS module is located behind the instrument panel, heating ducts and electrical wiring so that a thief would have to spend a considerable time to reach the module to disconnect it or modify it.
While at first blush it may appear that the fifteen resistor values are too few in number to achieve appreciable additional security, if the wrong resistor is selected, a time delay of from two to four minutes is imposed before the system will accept another resistance value. On the average, it will take seven or eight attempts before the correct resistor is randomly selected. This will cause the thief to be at risk of being caught for as long as a half an hour, long enough to deter many, but not all, thieves.
While VATS has provided increased security for vehicles in which it is installed, it has experienced numerous problems which prevent a legitimate owner from starting his automobile. These problems include: the resistor pellets falling out of the keys; bent electrical contacts in the lock often caused by the operator rotating the key before it is fully inserted in the lock; added series resistance due to corrosion of the electrical contacts resulting in invalid readings; fraying of the wires of the lock contacts which rotate every time the car is turned on or off and the expense and inconvenience of obtaining replacement or duplicate keys from locksmiths.
It has also been proposed to use a digital key in a security system in which the key is provided with a digital code which is optically read and compared to a code stored in a memory unit of the lock when the codes match. U.S. Pat. No 4,144,523 to Kaplit describes such a digital key system which includes circuitry responsive to a digital pulse train generated upon removal of the key from the lock for programming the digital key code into the lock memory as well as circuitry for reading the digital key code when a key is inserted in the lock, for comparing it to the code stored in the memory and for disabling the lock when the codes match. The digital code is placed on each key by the absence or presence of a hole in a first row of holes on the key. A similarly digitally encoded key system is described in International Patent Application PCT/GB86/00394 to O'Connell et al.
In both systems described by Kaplit and O'Connell et al., a second row of holes must be provided in the key to serve as a clock-track to control when a reading is made of the row of code holes to obtain the digital data. While O'Connell et al. use the word "may" implying that a clock-track is optional, there is no other way disclosed by them to insure accurate reading of the code row. A separate combination of a light emitting diode and photodetector are required to generate and receive optical signals for each row of holes on the key. The requirement for two rows of holes on the key to provide the code and clock-tracks necessitates that the holes be relatively small, thus increasing the tendency for the holes to be blocked by dirt or other foreign matter. In addition, in both systems described by Kaplit and O'Connell, the photoelectrical elements are disposed on the rotating lock core which presents the problem of failure due to wire fatigue when the lock is rotated over time, just as in the VATS system.
Accordingly, there remains a need in the art for a security system having particular application to motor vehicles, which provides heightened security without being subject to the problems which characterize existing security systems.